Intrinsic Chirality and Multispectral Spin‐Selective Transmission in Folded Eta‐Shaped Metamaterials

Abstract Manipulating light polarization is of fundamental importance in the modern photonic applications such as spectroscopy, laser science, optical communication, quantum information processing, chemical and biological sensing. Polarization control of light is typically achieved by natural chiral or birefringent materials with macroscopic volume due to the weak light–matter interaction. Here, a folded eta‐shaped metamaterial that is capable of generating gigantic optical chirality and spectrally breaking the spin degeneracy of optical transmission at multiband is experimentally demonstrated. The intrinsic chiral configuration is achieved by folding the eta‐shaped metasurface along the vertical direction to break the mirror symmetries. A remarkable circular dichroism approaching unity is experimentally achieved, with the maximum transmittance exceeding 93%. This is the record high value demonstrated to date for single‐layer metasurfaces without diffraction in infrared region. The folded metamaterial provides a straightforward strategy for achieving intrinsic 3D chirality and has great potential for applications in photon‐spin selective devices and chiral biomolecule identification.